In a gas turbine, air is pressurized by a compressor and then mixed with fuel and ignited within an annular array of combustors to generate hot gases of combustion. The hot gases flow from each combustor through a transition piece for flow along an annular hot gas path. Turbine stages are typically disposed along the hot gas path such that the hot gases flow through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The turbine buckets may be secured to a plurality of rotor disks comprising the turbine rotor, with each rotor disk being mounted to the rotor shaft for rotation therewith.
A turbine bucket generally includes an airfoil extending radially outwardly from a substantially planar platform and a shank portion extending radially inwardly from the platform for securing the bucket to one of the rotor disks. Additionally, many turbine buckets include a separate tip cap attached to the airfoil for sealing the airfoil tip. Currently, tip caps for turbine buckets are formed from metal-based materials, such as nickel- and cobalt-based superalloys. However, due to the extreme operating temperatures within a gas turbine, such metal-based tip caps must be continuously cooled to survive exposure to the hot gases combustion flowing over and/or around the airfoil tip. Accordingly, a portion of the working fluid of the gas turbine must be utilized to cool the tip cap, thereby decreasing the overall efficiency of the gas turbine. Moreover, metal-based tip caps are typically relatively heavy due to the high densities of metal-based material. As a result, these tip caps typically generate a significant load at the tip of the airfoil during operation, thereby increasing the stress acting on the turbine bucket.
Accordingly, a tip cap formed from a material with high temperature capabilities and/or low densities would be welcomed in the technology.